sedimentary
Chert (Jasper variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and cream; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
- Hardness
- 6
- Color
- Reddish-brown, tan, and cream
- Luster
- Dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, tan, and cream; Luster: Dull to waxy; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments; often found in nodules within limestone or as bedded deposits.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for lapidary work, jewelry, and landscaping gravel.
Geological facts
Chert was one of the most important minerals for prehistoric humans because its conchoidal fracture creates extremely sharp edges for spear points and knives.
Field identification & locations
Identify by its hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in riverbeds and sedimentary outcrops.
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Cone-in-cone structure (Secondary Sedimentary Structure)
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Chert Breccia
Brecciated Chert (Microcrystalline Silica)
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Clastic Sedimentary Rock Grain (SiO2 dominated)
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Shale or Slaty Mudstone
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Sandstone
Arenite (primarily SiO2)
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